Circuit arrangement having a transistor component and a freewheeling element

ABSTRACT

A circuit arrangement configured to drive a load is disclosed herein. The circuit arrangement comprises a first and a second supply potential terminal for application of a first supply potential and a second supply potential. A load terminal is provided between the first and second supply potential for connection of the load. The circuit arrangement further comprises a first transistor component of a first conduction type. The first transistor component includes a load path and a control terminal, with the load path connected between the first supply potential terminal and the load terminal. The circuit arrangement also comprises a freewheeling element. The freewheeling element is provided as a second transistor of a second conduction type connected up as a diode. The second transistor is connected between the load terminal and the second supply potential terminal. The first transistor component and the freewheeling element are integrated in a common semiconductor body.

FIELD

The present invention relates to a circuit arrangement for driving aload having a transistor component and a freewheeling element.

BACKGROUND

When driving a load using a transistor component it is generally knownto connect the transistor component in series with the load betweenterminals for first and second supply potentials or positive andnegative supply potentials. Such a circuit arrangement is illustrated inFIG. 1. In this case, the reference symbol M designates a transistorcomponent formed as a MOSFET, the load path of which is connectedbetween a first connecting terminal K1 for a first supply potential +Vand an output terminal OUT. A load L is connected between said outputterminal OUT and a second connecting terminal K2 for a second supplypotential GND, so that the load path of the transistor component M andthe load L are connected in series between the connecting terminals K1,K2 for the supply potentials. The load path of the MOSFET M is formed bythe drain-source path thereof. The MOSFET M can be driven via its gateterminal, which forms a control terminal, by a drive circuit 10according to a switching signal Sin. The drive circuit 10 is designed togenerate a drive signal Sdrv according to the switching signal Sin,which drive signal drives the MOSFET M in the on state or in the offstate according to the switching signal Sin.

An example of such a circuit arrangement having a transistor componentfor driving a load and a drive circuit for driving the transistorcomponent is the integrated device BTS 307 from Infineon TechnologiesAG, Munich, which belongs to the PROFET® family and is described in thedata sheet PROFET® BTS 307, Oct. 1, 2003, Infineon Technologies AG,Munich. In this arrangement, a transistor component formed as a powerMOSFET and the associated drive circuit are monolithically integrated ina semiconductor body/semiconductor chip.

If the transistor component M in the circuit in accordance with FIG. 1is driven in the on state, then the voltage drop across its load pathD-S is usually very small in comparison with the supply voltage presentbetween the connecting terminals K1, K2. The supply voltage is thuspresent approximately exclusively across the load L. When driving aninductive load, a considerable voltage loading on the semiconductorswitching element M may occur after the semiconductor switching elementM has been turned off, which voltage loading may be significantlygreater than the supply voltage, as is explained below with reference toFIG. 2.

It shall be assumed that the semiconductor switching element M is drivenin the on state depending on the switching signal Sin up to an instanttoff. The output voltage Vout present across the load L then essentiallycorresponds to the supply voltage +V. If the semiconductor switchingelement M is turned off at the switch-off instant toff, then uponcommutation of the inductive load L a voltage is induced which causesthe potential at the output terminal OUT to fall far below the referencepotential GND present at the second connecting terminal K2, so that thevoltage present across the semiconductor switching element M issignificantly higher than the supply voltage +V.

This fall in the potential at the output terminal OUT when thetransistor component M is turned off can be counteracted by connecting adiode D in parallel with the load L. This diode D has the effect that,upon commutation of the load L, the potential at the output terminal OUTfalls below the value of the reference potential GND at most by thevalue of the forward voltage of the diode. The diode D acts as afreewheeling element and accepts the freewheeling current flowing uponcommutation of the inductive load L.

What is disadvantageous about the previously explained solution is theneed to have to use an additional external component in the form of thediode D, which increases the production costs and the complexity in therealization of the circuit.

Therefore, it would be advantageous to provide a circuit arrangement fordriving a load, in particular for driving an inductive load, which has afreewheeling element and which can be realized simply andcost-effectively.

SUMMARY

A circuit arrangement is disclosed herein comprising a first and asecond supply potential terminal for application of a first and secondsupply potential and a load terminal for connection of the load. Thecircuit additionally comprises a transistor component of a firstconduction type having a load path and a control terminal, the load pathof which is connected between the first supply potential terminal andthe load terminal, and a freewheeling element, which is formed as atransistor of a second conduction type connected up as a diode and isconnected between the load terminal and the second supply potentialterminal. In this case, the transistor component and the freewheelingelement are integrated in a common semiconductor body.

On account of the integration of the freewheeling element together withthe transistor component in a common semiconductor body, thefreewheeling element can be realized cost-effectively and with littlecomplexity.

The transistor component is for example a power transistor formed as avertical MOSFET, while the freewheeling element is realized as a lateralMOSFET. The freewheeling element of the circuit arrangement can berealized for example by means of the same technology as components of anintegrated drive circuit of the power transistor.

The above described features and advantages, as well as others, willbecome more readily apparent to those of ordinary skill in the art byreference to the following detailed description and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention are explained in moredetail below with reference to figures.

FIG. 1 shows a circuit arrangement having a semiconductor switchingelement for driving a load according to the prior art.

FIG. 2 shows by way of example the profile of a switching signal and theprofile of a voltage present across the load for the circuit arrangementaccording to FIG. 1.

FIG. 3 shows an exemplary embodiment of a circuit arrangement having atransistor component and freewheeling element, which are integrated in acommon semiconductor body.

FIG. 4 shows a cross section through the semiconductor body forelucidating a freewheeling element in accordance with a first exemplaryembodiment.

FIG. 5 shows a cross section through the semiconductor body forelucidating a freewheeling element in accordance with a second exemplaryembodiment.

FIG. 6 shows a section through the semiconductor component in accordancewith FIG. 5 in a sectional plane A-A, and

FIG. 7 shows a sectional illustration corresponding to the sectionalillustration in FIG. 6 for elucidating a further exemplary embodiment ofthe freewheeling element.

In the figures, unless specified otherwise, identical reference symbolsdesignate identical components, component regions and signals with thesame meaning.

DESCRIPTION

FIG. 3 shows an exemplary embodiment of a circuit arrangement fordriving a load. This circuit arrangement has first and second supplypotential terminals K1, K2 for application of a first and second supplypotential +V, GND and a load terminal OUT for connection of a load L. Inorder to afford a better understanding, in the exemplary embodiment thefirst supply potential terminal K1 is connected to a positive supplypotential +V and the second supply potential terminal K2 is connected toa negative supply potential or reference potential GND.

The circuit arrangement additionally has a transistor component M, whichis formed as an n-channel MOSFET in the example. The drain-source pathof said MOSFET M forms the load path thereof and is connected betweenthe first supply potential terminal K1 and the load connecting terminalOUT. A load L, which is formed as an inductive load in the example, canbe connected between the load terminal OUT and the second supplypotential terminal K2, so that, with the load L connected, the load pathD-S of the MOSFET M is connected in series with the load L between thesupply potential terminals K1, K2.

The MOSFET M can be driven in the on state or in the off state by meansof a drive signal Sdrv. Said drive signal Sdrv is generated for exampleby a drive circuit 10 according to a switching signal Sin.

The circuit arrangement additionally has a freewheeling element, whichis formed as a p-channel MOSFET connected up as a diode in the exampleand is connected between the second supply potential terminal K2 and theload terminal OUT. With the load L connected, said freewheeling elementT2 is thus connected in parallel with said load L.

The p-channel MOSFET is connected up as a diode by virtue of its gateterminal G2 being short-circuited with its source terminal S2. The drainterminal D2 of the MOSFET T2 connected up as a diode is connected to thesecond supply potential terminal K2, while gate G2 and source S2 of theMOSFET T2 serving as a freewheeling element are jointly connected to thesource terminal S of the load transistor M.

The load transistor M and the MOSFET T2 connected up as a freewheelingelement are jointly integrated in a semiconductor body 100, which isillustrated schematically by a dash-dotted line in FIG. 3. The drivecircuit 10 that drives the load transistor M may suitably be integratedtogether with the load transistor M and the freewheeling element T2 inthe same semiconductor body 100.

FIG. 4 schematically shows a cross section through the semiconductorbody 100, in which the load transistor M and the freewheeling element T2are jointly integrated. The dopings of the semiconductor body in thecomponent regions that are yet to be explained in detail are chosen suchthat the load transistor M is an n-channel MOSFET and the freewheelingelement is a p-channel MOSFET. It goes without saying that the loadtransistor could also be realized as a p-channel MOSFET and thefreewheeling element as an n-channel MOSFET, in which case the dopingsexplained below should then be interchanged correspondingly, that is tosay that n-doped regions of the figures hereafter should becorrespondingly replaced by p-doped regions and p-doped regions shouldbe replaced by n-doped regions.

The semiconductor body 100 has a heavily n-doped semiconductor zone 11in the region of a rear side 102 of the semiconductor body 100. In thedirection of a front side 101 of the semiconductor body opposite to therear side 102, said heavily doped semiconductor zone 11 is adjoined by amore weakly n-doped semiconductor zone 12. The heavily dopedsemiconductor zone 11 may be realized by a semiconductor substrate, forexample, to which a more weakly doped epitaxial layer is applied, whichforms the more weakly doped semiconductor zone 12. Furthermore, it wouldalso be possible to provide a more weakly doped semiconductor body, thebasic doping of which corresponds to the doping of the more weakly dopedsemiconductor zone 12, and this semiconductor body could be more heavilydoped in the region of the rear side—for example by means of ionimplantation—in order to form the semiconductor zone 11.

In the example, the load transistor M is formed as a vertical powerMOSFET, the drain zone of which is formed by sections of the heavilydoped semiconductor zone 11 and the drift zone of which is formed bysections of the more weakly doped semiconductor zone 11. In order torealize this MOSFET, a p-doped body zone 21 is arranged in the region ofthe front side 101, a section of the more weakly doped semiconductorzone 11 adjoining said body zone in the vertical direction. Heavilyn-doped semiconductor zones 22, which form the source zones of the loadtransistor M, are arranged in said body zone 21. A gate electrode 23extends in a trench proceeding from the front side 101 in the verticaldirection into the semiconductor body 100 and is insulated from thesemiconductor regions by means of an insulation layer 24. The gateelectrode 23 comprises, for example, a highly doped polycrystallinesemiconductor material, for example polysilicon, and extends, in amanner insulated by the insulation layer 24, in the vertical directionproceeding from the source zones 22 through the body zone 21 right intothe more weakly doped semiconductor zone 12, which forms the drift zoneof the load transistor M. When a suitable drive potential is applied tothe gate electrode 23, a conducting channel forms in the body zone 21between the source zone 22 and the drift zone 12.

The load transistor M has a cellular structure, that is to say thatthere are a number of identically constructed structures present eachhaving a source zone 22, a gate electrode 23 and a section of the bodyzone 21 which is arranged adjacent to the gate electrode 23 and extendsfrom the source zone 22 to the drift zone 12. In this case, theindividual gate electrodes are electrically conductively connected toone another and connected to a gate terminal (illustratedschematically), each of these gate electrodes 23 serving for controllinga conducting channel between one of the source zones 22 and the driftzone 12. The source zones 22 of the load transistor M are jointlyconnected to a source terminal S, which is only illustratedschematically in FIG. 4. The body zone 21 may suitably beshort-circuited with the source zones 22, which is likewise illustratedschematically in FIG. 4.

In the more weakly doped semiconductor zone 12 of the semiconductor body100, which forms the drift zone of the load transistor M in the regionbelow the body zone 21, a p-channel MOSFET is realized in a mannerspaced apart in the lateral direction with respect to the componentstructure of the load transistor M. Said MOSFET is formed as a lateralMOSFET and has a p-doped drain zone 31 and a p-doped source zone 32arranged in a manner spaced apart from the drain zone 31 in the lateraldirection. The drain and source zones 31, 32 are in each case arrangedin the region of the front side 101 of the semiconductor body. A moreweakly p-doped semiconductor zone 33 adjoins the drain zone 31 in thelateral direction in the direction of the source zone 32, whichsemiconductor zone forms the drift zone of the p-channel MOSFET and thedoping and dimensions of which semiconductor zone critically determinethe dielectric strength of this p-channel MOSFET. A section of the moreweakly n-doped semiconductor zone 12 that is arranged between said driftzone 33 and the source zone 32 forms the body zone of said p-channelMOSFET. In the example, a gate electrode 34 of said p-MOSFET is arrangedabove the front side 101 and is insulated from the semiconductor body byan insulation layer 35.

The short circuit between the gate electrode 34 and the source zone 32that is required in order to realize the diode function is onlyillustrated schematically in FIG. 4. Gate G2 and source S2 of saidp-channel MOSFET are jointly connected to the source terminal S of theload transistor M in the manner elucidated. Said transistor is driven inthe on state when the potential at the drain terminal D2 rises above thepotential at the common source-gate terminal S2, G2 of said MOSFET bythe value of the threshold voltage of said MOSFET. The MOSFET therebyfunctions as a diode.

The p-channel MOSFET serving as a freewheeling element can be realizedin the same semiconductor body 100 as the load transistor M in a simplemanner. The realization of said freewheeling element may, in particular,be effected together with the realization of low-voltage components orlogic components which form the drive circuit 10 of the load transistorM. FIG. 4 illustrates a p-conducting transistor 11 and an n-conductingtransistor 12 as representative of the components of said drive circuit10. The p-conducting transistor has p-doped source and drain zones 111,112 spaced apart from one another. The body zone of said p-typetransistor is formed by a section of the more weakly doped semiconductorzone 12 that lies between source and drain 111, 112. A gate electrode113 of said transistor is arranged above the front side 101 in a mannerinsulated by an insulation layer 114. In order to realize then-conducting transistor 12, a p-doped well 120 is arranged in the regionof the front side 101 of the semiconductor body, n-doped source anddrain zones 121, 122 being realized in said well in a manner spacedapart from one another in the lateral direction. A gate electrode 123,which is arranged in a manner insulated from drain and source zones 121,122 by an insulation layer 124, serves for forming a conducting channelbetween source and drain zones 121, 122 in the p-doped body zone lyingbetween source 121 and drain 122.

The lateral p-channel MOSFET serving as a freewheeling element may alsobe realized in a corresponding manner during the method steps duringwhich the transistors 11, 12 are realized. The increased dielectricstrength of said lateral MOSFET in comparison with the dielectricstrength of the logic components 11, 12 results from the more weaklydoped drift zone 33 which adjoins the drain zone 31 in the lateraldirection and which is also referred to as a so-called drain extensionin the case of such a component. The channel width of this MOSFET is inthis case significantly greater than the channel width of the logictransistors which realize the drive circuit 10.

A further example for the realization of the p-channel MOSFET serving asa freewheeling element is explained below with reference to FIGS. 5 and6.

In this example, the gate electrode 34 of the MOSFET is formed in atrench extending into the semiconductor body 100 in the verticaldirection between drift zone 33 and source zone 32 proceeding from thefront side 101. In this case, the gate electrode 34 has a plurality ofelectrode sections which are arranged in a manner spaced apart from oneanother and are in each case insulated from the semiconductor zones byan insulation layer 35, as can be seen in particular from the crosssection through the sectional plane A-A in FIG. 6. A section of the moreweakly doped semiconductor zone 12 is in each case present between theindividual gate electrode sections and forms the body zone of thep-channel MOSFET in the region of the latter. When a suitable drivepotential is applied to the gate electrode sections 34, a conductingchannel forms in the n-doped body zone 12 between the drift zone 33 andthe source zone 32 along the electrode sections 34.

In order to further increase the dielectric strength of the p-channelMOSFET, there is the possibility, referring to FIG. 6, of forming thep-channel transistor as a compensation component. For this purpose,n-doped semiconductor zones 34 which are formed in pillar-type fashionand extend into the semiconductor body in the vertical directionproceeding from the front side 101 are produced in the p-doped driftzone 33. These semiconductor zones 34 doped complementarily to the driftzone 33 are illustrated in plan view in FIG. 6. These pillar-typesemiconductor zones have a circular cross section, for example, that mayalso have a square or arbitrary polygonal cross section.

FIG. 7 shows, in a sectional plane corresponding to the sectional planein accordance with FIG. 6, a further exemplary embodiment of thep-channel MOSFET serving as a freewheeling element. This MOSFET differsfrom the one illustrated in FIG. 6 by virtue of the fact that thetrenches with the gate electrodes 34 arranged therein extend far intothe drift zone 33 in the lateral direction. In this case, the trenchesmay reach as far as the boundary with the drain zone 31 or even rightinto the drain zone 31. The gate electrodes fulfill the function offield plates 37 in the region of the drift zone and are surrounded by athicker insulation layer 35 there than in the region of the body zone12. This is achieved in the example by virtue of the fact that the gateelectrodes taper in the region of a drift zone 33, while the trencheshave an at least approximately identical width over their entire length.The distance between the individual trenches with the gate electrodes 34or field plates 37 arranged therein and the doping of the p-type driftzone are co-ordinated with one another such that the p-type dopant dosebetween two trenches in a direction R perpendicular to the longitudinalextent of the trenches is less than 2·10¹² cm⁻².

With the component being driven in the on state, when the electricalpotential of the field electrodes is lower than the potential in thedrift zone 33, the field electrodes 37 bring about an accumulation ofp-type charge carriers in the drift zone 33 and thus reduce the onresistance of the component in comparison with the component withoutsuch field electrodes. Only the doping of the drift zone and the extentthereof in the lateral direction are critical, by contrast, for theblocking capability of the component.

While the invention disclosed herein has been described in terms ofseveral preferred embodiments, there are numerous alterations,permutations, and equivalents which fall within the scope of thisinvention. It should also be noted that there are many alternative waysof implementing the methods and compositions of the present invention.It is therefore intended that the following appended claims beinterpreted as including all such alterations, permutations, andequivalents as fall within the true spirit and scope of the presentinvention.

1. A circuit arrangement for driving a load, the circuit arrangementcomprising: a first supply potential terminal, a second supply potentialterminal, and a load terminal, the first supply potential terminalconfigured for application of a first supply potential, the secondsupply potential terminal configured for application of a second supplypotential, and the load terminal configured for connection of the load;a first transistor component of a first conduction type, the firsttransistor component having a load path and a control terminal, the loadpath connected between the first supply potential terminal and the loadterminal; and a freewheeling element provided as a second transistorcomponent of a second conduction type, the second transistor componentconnected between the load terminal and the second supply potentialterminal, the first transistor component and the second transistorcomponent being integrated in a common semiconductor body.
 2. Thecircuit arrangement of claim 1 wherein the first transistor component isa vertical MOSFET and the second transistor component is a lateralMOSFET.
 3. The circuit arrangement of claim 2 wherein the firsttransistor component and the second transistor component each include adrain zone, a drift zone, a body zone and a source zone, wherein thedrift zone of the first transistor component and the body zone of thesecond transistor component are formed by a common semiconductor zone.4. The circuit arrangement of claim 3 wherein the drain zone of thefirst transistor component is arranged in a rear side region of thesemiconductor body, and wherein the source zone of the first transistorcomponent is arranged in a front side region of the semiconductor body.5. The circuit arrangement of claim 3 wherein the drain zone, the driftzone, the body zone, and the source zone of the second semiconductorcomponent are arranged in a front side region of the semiconductor body.6. The circuit arrangement of claim 1 wherein the first transistorcomponent is an n-channel MOSFET and the second transistor component isa p-channel MOSFET.
 7. The circuit arrangement of claim 6 wherein thefirst transistor component and the second transistor component eachinclude a drain zone, a drift zone, a body zone and a source zone,wherein the drift zone of the first transistor component and the bodyzone of the second transistor component are formed by a commonsemiconductor zone.
 8. The circuit arrangement of claim 7 wherein thedrain zone of the first transistor component is arranged in a rear sideregion of the semiconductor body, and wherein the source zone of thefirst transistor component is arranged in a front side region of thesemiconductor body.
 9. The circuit arrangement of claim 7 wherein thedrain zone, the drift zone, the body zone, and the source zone of thesecond semiconductor component are arranged in a front side region ofthe semiconductor body.
 10. The circuit arrangement of claim 1 furthercomprising a drive circuit, the drive circuit connected to the controlterminal of the first transistor component and integrated in the commonsemiconductor body with the first transistor component and the secondtransistor component.
 11. The circuit arrangement of claim 1 wherein thesecond transistor is operable to act as a diode between the loadterminal and the second supply potential terminal.
 12. The circuitarrangement of claim 11 wherein the second transistor includes a firstterminal, a second terminal, and a control terminal, wherein the controlterminal of the second transistor is short circuited with the firstterminal of the second transistor.
 13. A circuit arrangement comprising:a first supply potential; a second supply potential; a load providedbetween the first supply potential and the second supply potential; afirst transistor of a first conduction type, the first transistorincluding a load path and a control terminal, the load path connectedbetween the first supply potential and the load; a second transistor ofa second conduction type, the second transistor including a firstterminal, a second terminal and a control terminal, the first terminalconnected between the load path of the first transistor and the load,the second terminal connected to the second supply potential, and thecontrol terminal of the second transistor connected to the firstterminal, wherein the first transistor and the second transistor areintegrated in a common semiconductor body.
 14. The circuit arrangementof claim 13 wherein the first transistor is a vertical MOSFET and thesecond transistor is a lateral MOSFET.
 15. The circuit arrangement ofclaim 13 wherein the first transistor is an n-channel MOSFET and thesecond transistor is a p-channel MOSFET.
 16. The circuit arrangement ofclaim 13 further comprising a drive circuit, the drive circuit connectedto the control terminal of the first transistor and integrated in thecommon semiconductor body with the first transistor and the secondtransistor.
 17. A circuit arrangement comprising: a first supplypotential terminal, a second supply potential terminal, and a loadterminal, the first supply potential terminal configured for connectionto a first supply potential, the second supply potential terminalconfigured for connection to a second supply potential, and the loadterminal configured for connection to a load; a first transistorcomponent including a load path and a control terminal, the load pathconnected between the first supply potential terminal and the loadterminal; and a second transistor including a source terminal, a drainterminal and a gate terminal, the source terminal connected to the loadterminal, the drain terminal connected to the second supply potentialterminal, and the gate terminal connected to the source terminal. 18.The circuit arrangement of claim 17 wherein the first transistor and thesecond transistor are integrated in a common semiconductor body.
 19. Thecircuit arrangement of claim 18 further comprising a drive circuit, thedrive circuit connected to the control terminal of the first transistorand integrated in the common semiconductor body with the firsttransistor and the second transistor.
 20. The circuit arrangement ofclaim 17 wherein the first transistor is of a first conduction type andthe second transistor is of a second conduction type.